Asynchronous Transfer Mode (ATM) is a telecommunications concept defined by standards established by the American National Standard for Telecommunications (ANSI) and the International Telephone and Telegraph Consultative Committee (CCITT), a predecessor standards committee to the International Telecommunication Union (ITU), for carriage of a complete range of user traffic, including voice, data and video signals on any User-to-Network Interface (UNI) and to facilitate multi-media networking between high speed devices such as workstations, super computers, routers or bridges. The user network interface converts from one protocol, such as SONET, DS-3, to another such as ATM in going between, in this case, telephone communication lines and an ATM system such as a LAN. In this case, the telephone communications protocol and the ATM system employed at the User Network Interface are called the physical layers and the UNI is called the physical layer device. The physical layer is the lowest level of communication between networks or within a network. The physical layer also communicates with the next highest layer, the ATM layer. Thus, in considering a system consisting of a central office and a network, the physical layer would include the transmission lines or physical medium along which the information travels from central office to the network and back. Alternately, the physical layer within a network could be the physical medium which carries information to and from a given station and interfaces with the next higher layer, which is an ATM layer, for that station. Information would then go to and from the ATM layer, to and from an adaptation layer device and then to and from an end user.
ATM switches are required in order to direct ATM cells between end users, between end users in one ATM network and those in another or from end users in one network through a public network to those in another network. On each side of an ATM switch there is an ATM layer device which performs various functions such as cell identification, translation, policing, monitoring and management.
A cell bus operating according to specifications known by the acronym UTOPIA is widely employed on physical devices in view of its simplicity. The UTOPIA specification provides 53 bytes of 8 bit wide bytes or 16 bit wide words with 27 words per cell.
Accordingly, it is an object of the invention to provide a single ATM layer device which performs all of the functions required in interfacing between an ATM physical layer device and an ATM switch. It is a further object of the invention to utilize a standard UTOPIA cell bus interface in the connection between the physical layer device and the ATM switch core.